Electro-hydraulic pilot stages are known in the art. In a conventional arrangement, a magnetic torque motor (utilizing a magnet, a coil, a magnetic plate, and magnetic pole pieces) is used to control movement of an armature. The movement of the armature in turn produces movement in a separate flapper that is coupled to the armature.
The coupling between the armature and flapper is a torsion pivot arrangement (a torsion bar or torsion tube is often utilized in the industry). In response to the movement of the flapper, a pressure differential is created between the output of two nozzles that are positioned in close proximity to the flapper. The differential pressure balances the torque applied to the armature.
It can be appreciated that the use of a separate armature in combination with a flapper adds complexity to the pilot stage. In order to control the movement of a flapper, the movement of the armature must be controlled. This requires an understanding of the interrelationship between the flapper and the armature. In addition, the use of an armature which is a separate piece from the flapper adds to the cost of the pilot stage by requiring two distinct parts. In a similar manner, the use of a torsion pivot also adds to the cost of the valve. There is a need in the art for an electro-hydraulic pilot stage which does not require a torsion pivot or an armature which is separate from the flapper.
Therefore, it is a primary object of the present invention to provide an improved electro-hydraulic pilot stage.
It is a further object of the present invention to provide an electro-hydraulic pilot stage that utilizes a single flapper to perform the same function that has previously been performed by a flapper in conjunction with a separate armature.
A further object of the invention is to provide a pilot stage which eliminates the need for a torsion pivot (plate or tube).
An additional object of the present invention is to provide an electro-hydraulic pilot stage of greater reliability and consistency.
An additional object of the present invention is to provide differential pressure proportional to input current without utilizing a permanent magnet.
A still further object of the present invention is to provide an electro-hydraulic pilot stage which is economical to manufacture, durable in use, and efficient in operation.
These, as well as other objects and features of the present invention, will be apparent from the following detailed description and claims in conjunction with the accompanying drawings.
The present invention includes an improved pilot stage. The pilot stage has first and second nozzles which are connectable to a fluid supply. The pilot stage also has a flapper having first and second ends. The ends of the flapper are in fluid communication with the nozzles. The pilot stage additionally includes a magnetic torque motor having a coil that is connectable to an electrical energy source. The coil is magnetically coupled to the first end of the flapper. When an input current is supplied to the coil, the flapper will pivot. The pivotal movement of the flapper brings one end of the flapper closer to one of the nozzles, creating a pressure differential between the nozzles. A second coil can be provided so that the flapper can be pivoted in two directions, thereby obtaining a differential pressure in both directions, proportional to the input current.
The pressure differential acts on the flapper, counteracting the torque provided by the magnetic torque motor.